This invention relates to optic switches for use in building an optical communication network and, more particularly, to a mechanical optic switch for controlling optical coupling among a plurality of optical fibers by mechanically moving or repositioning a mirror and also to a method of manufacturing such an optic switch.
Rapid growth of fiber optic communication networks has been giving rise to demands for numerous optical components including optic switches. A low-cost optical component is important for a large-scale communication network and a local area network (LAN) which rest on optical fibers.
Of late, interests have been taken in the use of micro-machining technique to improve the performance, and to reduce the cost, of a mechanical optic switch. Of especial importance is the ability of the micro-machining technique to manufacture a large number of optical matrix switches capable of switching among their inputs and outputs one to another, integrally on a single chip. Such an optical matrix switch is a most important component that is wanted in a dynamically reformable, high density, wavelength division, multiplex communication network.
In the conventional optic switch, there are a plurality of mutually different primary factors or causes which deteriorate its performance. A matrix switch, in which errors and uncertainties included in these factors and causes cumulate to deteriorate its performance, has greater impact from such factors and causes than a single switch. Of those factors and causes, the most important is seen from an optical standpoint. Indeed, conventional optic switches have several problems, one of which is that because of their poor mirror surface quality they are unusable in an application that requires multiple reflection. Another problem is that when made up of individual components such as optical fibers and a mirror in combination, a conventional optic switch is insufficient in the accuracy of alignment with an optical axis between the mirror and fiber orienting structures. Thus, for each of the optical fibers, fine adjustment is required of its optical axis with the result that these fine adjustments are costly.
Employing Si micromachining technique can solve these problems. However, while optic switches have so far been made by the conventional micromachining technique by using deep excavating reactive ion etching, surface micromachining or bulk micromachining, no mechanical optic switch has as yet been obtained that is of enough performance.
For example, optic switches made by deep excavating reactive ion etching have the problem that they have ripples (wavy irregularities) formed on their vertical surfaces, which when they are used as mirrors cause an increase in optical loss.
An optic switch has also been made by surface micromachining. While an optic switch by surface micromachining is manufactured by opto-axially aligning a mirror, micro-lenses and optical fibers, subtle variations caused for an optical axis every manufacture, which call for aligning the optical axis for each of the components of an optic switch manufactured in advance of its utilization, make it impossible to manufacture a large number of such optic switch products in a batch work without requiring fine axial adjustments.
It may also be noted that bulk micromachining makes it possible to form an optical component self-aligned in accordance with a crystallographically oriented face dependent etching process.
To make an optic switch by the use of bulk micromachining, while it has indeed been reported to so micromachine a (110) crystallographic face silicon wafer and then to use its (111) face vertical wall for a mirror, it has not been made possible to form a V-groove for fiber alignment.
As another example of forming an optic switch by the use of bulk micromachining, it has been reported to use a (100) face silicon wafer and then to form both a mirror and a fiber aligning structure self-aligned and to use its (100) face vertical wall for the mirror. However, while this can be used to provide such a passive device as a beam splitter, the same has been inapplicable to a mechanical switch having a mirror made mechanically movable to controllably establish optical coupling between two of a plurality of optical fibers.
In sum, therefore, it has so far been altogether difficult to manufacture a mechanical optic switch with input and output optical fibers and a movable mirror in opto-axial alignment with due accuracy. Consequently, the problem has been had of necessitating fine opto-axial pre-adjustments of the optic switch before its use. The problem has also been had that insufficiency in mirror surface smoothness causes large insertion loss.
This invention is provided to solve the above-mentioned problems met in the prior art and has for its first object to provide a mechanical optic switch that is high in the accuracy of opto-axial alignment for a mirror and a fiber aligning structure and yet is low in insertion loss.
A second object of this invention is to provide a method of its manufacture that makes its production cost dramatically low.
In order to achieve the first object mentioned above, there is provided in accordance with the present invention, a mechanical optic switch, characterized in that it comprises a groove for fixing an optical fiber, and a movable mirror, wherein the said groove and the said mirror are those formed simultaneously in a single crystal substrate in accordance with a crystallographically oriented face dependent etching process.
In the construction mentioned above, the said groove for fixing an optical fiber may be a V-groove, and the said movable mirror may comprise a resilient support beam capable of flexing or deflection and a mirror made integrally with the said resilient support beam.
Further, the said V-groove may be formed of a Si (111) crystallographic face and the said mirror may have a mirror surface formed of a Si (100) crystallographic face.
The construction mentioned above makes it possible for the optical axes of such optical fiber fixing grooves and the movable mirror to be established independently of the accuracy of etching masks and the time period of etching but at an accuracy as determined by the accuracy of crystallographic faces"" orientations, thus permitting the optical fibers and the mirror to be aligned opto-axially at high accuracy. Moreover, the mirror surface formed by crystallographically oriented face dependent etching is flat and even at the accuracy of a crystallographically oriented face and therefore reduces the loss of light to a minimum.
Further, the ability for the resilient support beam to be deflected by an external force applied thereto enables the mirror surface selectively to come out of the optical axis of an optical fiber, which in turn enables the optical path to be altered one to another among a plurality of optical fibers and also to be restored by removing the external force; hence optical switching operations made possible.
Further, in the mechanical optic switch according to the present invention, the said movable mirror may have a permanent magnet disposed on a rear surface of the said resilient support beam capable of flexing, and a drive coil or a yoke including drive coil that is disposed beneath the said permanent magnet and adapted to be supplied with an electric current to create a magnetic field for driving the said movable mirror.
Still further, the switch may be so constructed that adding the permanent magnet to the said yoke including drive coil establishes a pair of stable positions for the said resilient support beam having the permanent magnet disposed on the rear surface thereof, and that directionally reversing the electric current passed through the said coil selectively establishes one of the said two stable positions.
According to this construction, a magnetic field is created by the drive coil when an energizing current is turned on therethrough. And, the resilient support beam is then deflected by the virtue of this magnetic field exerted on the magnet attached thereto to bring the mirror surface out of the optical axes of the optical fibers, thus changing the optical path among a plurality of optical fibers from one to another. Also, removing the magnetic field by turning the energizing current off though the drive coil causes the resilient support beam to restore its undeflected position by its elastic restoring energy and returns the mirror to its original position, thus returning the optical path among the optical fibers to the original. Therefore, an optical switching operation is made possible.
Also, the construction in which a permanent magnet is added to a drive coil or a yoke including drive coil permits the drive coil to be supplied with energizing current only at the moment at which one of the two stable states corresponding to the ON and OFF of the optic switch is switched to the other. Consequently, there becomes possible optical switching with a minimum consumption of electric power.
In order to achieve the second object above, the present invention provides a method of manufacturing a mechanical optic switch, which method is characterized in that it comprises applying a crystallographically oriented face dependent etching process to simultaneously form in a Si (100) crystallographically faced single crystal substrate, a V-groove for fixing an optical fiber and a movable mirror made of an resilient support beam and a mirror.
In the construction mentioned above, the crystallographically oriented face dependent etching process is performed after there has been formed on the said Si (100) crystallographically faced single crystal substrate, an etching mask pattern comprising a region of rectangular open pattern for the said resilient support beam, a region of rectangular masking pattern in the said region of rectangular open pattern for the said mirror, and a plurality of regions of open pattern for such V-grooves as aforesaid.
Also, in the construction mentioned above, the said region of rectangular open pattern for the said resilient support beam and the said region of rectangular masking pattern in the said region of rectangular open pattern for the said mirror may each be of a rectangle lying in a (100) crystallographic plane and having one side oriented in a  less than 100 greater than  crystallographic direction or in a direction equivalent thereto and other side perpendicular to the said one side.
The said plurality of regions of rectangular open pattern for V-grooves are each a region of rectangular open pattern lying in the (100) crystallographic plane and having a longitudinal axis oriented in the  less than 100 greater than  crystallographic direction or in a direction equivalent thereto and are each arranged having the said longitudinal axis directed towards a center of the said region of masking pattern for the said mirror and are so arranged as to surround the said region of rectangular open pattern for the said resilient support beam.
Also, a slit corresponding in shape and depth to the shape and thickness of the said resilient support beam is made by etching from a rear surface of the said single crystal substrate to render the said support beam resilient and capable of flexing or deflection.
According to this construction, the open pattern for the resilient support beam and the rectangular masking pattern in this open pattern for the mirror permit the (100) crystallographic face or a face equivalent thereto to be kept exposed for etching and allow etching to proceed both in the direction of depth and sideways. And, controlling the etching time period makes it possible to form monolithically or in one piece both a mirror with a mirror surface constituted by the (100) crystallographic face and having a predetermined thickness and a support beam portion becoming a resilient support beam having a shape and a thickness predetermined. This etching operation may either be preceded or followed by slitting by etching from the rear side of the single crystal substrate to separate from the single crystal substrate the periphery of the support beam portion except for its base portion, namely a region where the resilient support beam is connected to the single crystal substrate. This renders the support beam portion resilient and capable of deflection, becoming the resilient support beam or cantilever beam. The V-grooves, each of which is composed by the (111) crystallographic face or a face equivalent thereto are formed with a shape as determined by the width of the open etching pattern alone and essentially independent of the etching time period.
In this manner, the method according to the present invention of manufacturing a mechanical optic switch can be used to produce a mechanical optic switch of the present invention at a dramatically reduced production cost.